Fixes to package.json

The latest version of libcoin on npm is outdated. I have upped the version number so that all of the changes can be uploaded to npm. Also, I have made two other changes:

1) I have removed "main: index" since there is no index.js file. As far as I can tell there is no main entry point into libcoin so there should be no "main" in package.json.

2) I have edited all dependences so they specify exactly which version number should be used. This ensures that any changes to the behavior of dependencies can't break libcoin, but is also means security changes to dependencies won't filter down unless you specifically include the new versions in libcoin. It's a trade off.